1. Field of the Invention
The present invention generally relates to switched electronic devices with hysteresis control, and more particularly, to switched-mode power supplies (or SMPS) of this type.
The invention is applicable, in particular, to switched-mode power supplies for supplying power to automobile vehicle electronic control units.
2. Description of the Related Art
Hysteresis switched-mode power supplies are switched electronic devices, typically controlled by a Pulse Width Modulation (or PWM) signal with two states, whose changes of state result from the comparison of a controlled value with a low threshold and with a high threshold.
This signal has a control frequency which varies as a function of the operating point (voltage, current). With a substantially constant output voltage, it varies in a continuous manner with the value of the output current. The higher the output current absorbed by the load, the higher the control frequency. For this reason, this control frequency may go into specific bands of frequencies and end up at a non-compliance with the specifications in terms of electromagnetic compatibility (EMC) when the product is qualified. These bands of frequencies are referred to as “forbidden”.
Switched-mode power supplies are therefore designed and component values chosen so as to operate up to a maximum “authorized” frequency, which is below the lowest forbidden band of frequencies. This generally allows the requirements in terms of EMC to be guaranteed.
This result is however obtained at the expense of difficult compromises between the requirements relating to the desired ranges of operation (current, voltage), and to the economically acceptable values of the most critical components of the switched-mode power supply, more particularly of the inductor and of the capacitor. This is because limiting the frequency of operation requires the use of components having high values, hence costly and furthermore bulky, in order to obtain certain operating points at high currents and/or voltages.